In the field of microfabrication represented by fabrication of IC chips, the design rules have become more and more stringent in order to achieve higher integration of the circuits. Development of a lithographic process enabling microfabrication in a stable manner has been actively pursued. However, since it has been difficult to form micro patterns of 22 nm or less with high precision by a general method of using KrF or ArF excimer lasers, a method of using EB or EUV has been proposed.
As a radiation-sensitive resin composition used for a positive-tone resist agent using EB or EUV for use in ultra-microfabrication, (1) a chemically amplified radiation-sensitive resin composition containing a polyhydroxystyrene resin partially protected by an acid-dissociable functional group (a resin for KrF excimer), a novolak resin (a resin for i-lines), and an acid generator and (2) a methacryl main chain cut-type radiation-sensitive resin composition containing PMMA (polymethyl methacrylate) and the like have been disclosed.
As specific examples of the composition (1), a composition containing a polyhydroxystyrene resin partially protected by an acetal group and an acid generator having well-balanced high sensitivity, high resolution, and high etching resistance (see Patent Document 1), a composition containing polyhydroxystyrene resin partially protected by various acid dissociable groups, an onium salt which generates a fluorine-containing aromatic sulfonic acid, and a fluorine-containing or silicon-containing surfactant (see Patent Document 2), an onium salt having at least one electron attractive group (a fluorine, a cyano group, a nitro group, etc.) as a substituent of a cation moiety (see Patent Document 3), a resin having a disulfonyl group (see Patent Document 4), a resin having an N-oxyimidesulfonyl group (see Patent Document 5), and the like have been disclosed. However, these methods have not still reached a practical use level in surface roughness during micro-pattern formation, sensitivity, and resolution.
On the other hand, the methacryl main chain cut-type radiation-sensitive resin composition (2) is excellent in resolution, but has problems in etching resistance, sensitivity, and outgassing. Therefore, it is difficult to use this resin composition in practice. In addition to these compositions, poly-t-butyl-α-chloromethylstyrene excellent in balance of resolution and sensitivity (Patent Document 6) and a resin with an atom (N, O, S) which is cut with ease by electron beams introduced into the resin terminal (Patent Document 7) have been disclosed. However, although some improvement may be recognized in sensitivity, the resins still have problems in sensitivity, etching resistance, and outgassing. These resins therefore have not yet reached a practically usable level.    [Patent Document 1] JP-A-6-194842    [Patent Document 2] JP-A-2000-187330    [Patent Document 3] JP-A-2001-075283    [Patent Document 4] JP-A-2002-072483    [Patent Document 5] JP-A-2002-107920    [Patent Document 6] JP-A-2000-147777    [Patent Document 7] JP-A-11-29612